Polybenzoxazine that can be used for coating metal and for the bonding of same to rubber

ABSTRACT

Polybenzoxazine comprises repeat units which comprise at least one unit corresponding to the formulae (I) or (II):in which Z1 and Z2, which are identical or different, represent an at least divalent, aliphatic, cycloaliphatic or aromatic bonding group comprising at least one carbon atom and optionally at least one heteroatom selected from O, S, N and P. Such a polybenzoxazine may be used as a metal-adhesive layer, in particular for the adhesive bonding of a metal substrate, in particular made of carbon steel, to a rubber.

1. FIELD OF THE INVENTION

The present invention relates to thermosetting resins, which can be usedin particular in adhesive systems intended in particular for theadhesive bonding of metal to rubber.

The invention relates more particularly to the polymers havingbenzoxazine units or “polybenzoxazines” that can be used in particularas adhesive layers in metal/rubber composites intended for themanufacture of rubber articles such as pneumatic or non-pneumatic tyres,for motor vehicles.

2. PRIOR ART

Metal/rubber composites, in particular for motor vehicle tyres, are wellknown. They are usually composed of a matrix made of unsaturated rubber,generally diene rubber, which can be crosslinked with sulfur, comprisingmetal reinforcing elements (or “reinforcers”) such as wires, films,tapes or cords made of carbon steel.

As they are subjected to very high stresses during the running of thetyres, especially to repeated actions of compression, bending orvariation in curvature, these composites must, in a known way, satisfy alarge number of sometimes contradictory technical criteria, such asuniformity, flexibility, flexural strength and compressive strength,tensile strength, wear resistance and corrosion resistance, and mustmaintain this performance at a very high level for as long as possible.

It is easily understood that the adhesive interphase between rubber andreinforcers plays a predominant role in the endurance of thisperformance. The conventional process for connecting the rubbercompositions to carbon steel consists in coating the surface of thesteel with brass (copper/zinc alloy), the bonding between the steel andthe rubber matrix being provided by sulfurization of the brass duringthe vulcanization or curing of the rubber. In order to improve theadhesion, use is generally made, in addition, in these rubbercompositions, of organic salts or metal complexes, such as cobalt salts,as adhesion-promoting additives.

In point of fact, it is known that the adhesion between the carbon steeland the rubber matrix is capable of weakening over time as a result ofthe gradual development of sulfides formed under the effect of thevarious stresses encountered, especially mechanical and/or thermalstresses, it being possible for the above decomposition process to beaccelerated in the presence of moisture. Moreover, the use of cobaltsalts renders the rubber compositions more sensitive to oxidation and toageing, and significantly increases the cost thereof, not to mentionthat it is desirable to eliminate, in the long run, the use of suchcobalt salts in rubber compositions due to the recent change in Europeanregulations relating to metal salts of this type.

For all the reasons set out above, manufacturers of metal/rubbercomposites, in particular motor vehicle tyre manufacturers, are seekingnovel adhesive solutions in order to adhesively bond metal reinforcersto rubber compositions, while overcoming, at least in part, theabovementioned disadvantages.

Thus, the recently published applications WO 2014/063963, WO2014/063968, WO 2014/173838, WO 2014/173839, filed by the applicantcompanies, have described novel polymers with urea, urethane or thioureaunits, and also the initial monomers thereof, which meet the aboveobjectives. Used in particular as adhesion primer on metal inmetal/rubber composites, these polymers make it possible veryadvantageously to adhesively bond the metal to the rubber matrices bysubsequently using simple textile adhesives, such as “RFL”(resorcinol/formaldehyde latex) adhesives or other equivalent adhesivecompositions, or else directly (that is to say, without employing suchadhesives) to these rubber matrices when the latter contain, forexample, appropriate functionalized unsaturated elastomers, such asepoxidized elastomers. Thus, the cobalt salts (or other metal salts) canin particular be dispensed with in the rubber compositions intended tobe connected to brass-coated metal reinforcers.

In continuing their research, the applicant companies have found a novelpolymer, of thermosetting type, which at ambient temperature has thesame adhesive performance, with respect to metal and rubber, as theaforementioned polymers but which has, once thermoset (crosslinked),further improved thermal and chemical stability. Moreover, its specificmicrostructure makes it possible very advantageously to adjust theflexibility of the molecule depending on the particular applicationstargeted.

3. BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a polybenzoxazine comprising at leastrepeat units comprising at least one unit corresponding to the formulae(I) or (II):

in which Z₁ and Z₂, which are identical or different, represent an atleast divalent, aliphatic, cycloaliphatic or aromatic bonding groupcomprising at least one carbon atom and optionally at least oneheteroatom selected from O, S, N and P.

The invention also relates to the use of such a polymer as coating of asubstrate at least the surface of which is at least partially metallic,in particular for the adhesive bonding of such a substrate to a rubber.

The invention also relates to any substrate at least the surface ofwhich is at least partially metallic, at least said metallic part beingcoated with the polymer according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

The invention and the advantages thereof will be easily understood inthe light of the detailed description and exemplary embodiments whichfollow, and also of the FIGS. 1 to 22 relating to these examples, whichrepresent or depict:

-   -   the general principle for synthesis of a benzoxazine compound        from three compounds, phenol, formaldehyde and amine (R=residue        of the amine) (FIG. 1a );    -   the (ring-opening) mechanism for opening, by heat input, the        oxazine ring of such a benzoxazine compound (FIG. 1b );    -   a general scheme for the synthesis, starting from a halogenated        phenol (the symbol Hal representing a halogen), paraformaldehyde        and a diamine, of a halogenated benzoxazine of formula (A)        (Monomer denoted by M) that can be used for the synthesis of a        polybenzoxazine in accordance with the invention (FIG. 2);    -   a possible scheme for the synthesis, starting from a halogenated        phenol, p-formaldehyde and a specific diamine, of aliphatic        type, of a particular halogenated benzoxazine of formula (A-1)        (Monomer denoted by M-1) that can be used for the synthesis of a        polybenzoxazine in accordance with the invention (FIG. 3);    -   another possible scheme for the synthesis, starting from a        halogenated phenol, p-formaldehyde and another specific diamine,        of aromatic type, of another example of a particular halogenated        benzoxazine of formula (A-2) (Monomer denoted by M-2) that can        be used for the synthesis of another polybenzoxazine in        accordance with the invention (FIG. 4);    -   three other possible schemes for the synthesis, starting from a        halogenated phenol, p-formaldehyde and specific diamines that        are all aliphatic, of other examples of particular halogenated        benzoxazines of respective formulae (A-3), (A-4) and (A-5)        (Monomers denoted by M-3, M-4 and M-5) that can be used for the        synthesis of other polybenzoxazines in accordance with the        invention (FIG. 5, FIG. 6 and FIG. 7);    -   another possible scheme for the synthesis, starting from a        halogenated phenol, p-formaldehyde and a specific aliphatic        triamine, of another example of a particular halogenated        benzoxazine of formula (A-6) (Monomer denoted by M-6) that can        be used for the synthesis of another polybenzoxazine in        accordance with the invention (FIG. 8);    -   a general scheme for the synthesis of a polybenzoxazine polymer        (Polymer denoted by P) according to the invention, starting from        the halogenated benzoxazine of formula (A) (Monomer M) from FIG.        2 and another halogenated benzoxazine (Monomer M′) of generic        formula (A′) (FIG. 9);    -   a scheme for the synthesis of a particular polybenzoxazine        polymer (Polymer denoted by P-1) according to the invention,        starting from a particular halogenated benzoxazine of formula        (A-7) (Monomer M-7) and another particular halogenated        benzoxazine (Monomer M-7′) of formula (A-7′) (FIG. 10);    -   a scheme for the synthesis of another polybenzoxazine (Polymer        denoted by P-2) according to the invention, starting from the        particular halogenated benzoxazine of formula (A-7) (Monomer        M-7) from the preceding FIG. 10 and another particular        halogenated benzoxazine of formula (A-8) (Monomer M-8) (FIG.        11);    -   a scheme for the synthesis of another polybenzoxazine (Polymer        denoted by P-3) according to the invention, starting from the        halogenated benzoxazine of formula (A-7) (Monomer M-7) and        another particular halogenated benzoxazine of formula (A-9)        (Monomer M-9) (FIG. 12);    -   the polybenzoxazine (Polymer denoted here by P′) according to        the invention from FIG. 9 once the oxazine rings thereof have        been opened after heat treatment of the Polymer P (FIG. 13);    -   the particular polybenzoxazine (Polymer denoted by P-1′)        according to the invention of FIG. 10, once the oxazine rings        thereof have been opened after heat treatment of the Polymer P-1        (FIG. 14);    -   the scheme for the synthesis, starting from brominated phenol        (compound 1), p-formaldehyde (compound 3) and a specific        aliphatic diamine (compound 2), of a particular brominated        dibenzoxazine of formula (A-10) (Monomer denoted by M-10) that        can be used for the synthesis of polybenzoxazines (Polymer P-4        and P-4′ from FIG. 17) in accordance with the invention (FIG.        15);    -   the ¹H NMR spectrum (500 MHz) of Monomer M-10 dissolved in        CD₂Cl₂ (FIG. 16);    -   the scheme for the synthesis of a particular polybenzoxazine        (homopolymer) (Polymer denoted by P-4) according to the        invention, starting from the sole particular halogenated        benzoxazine of formula (A-10) (Monomer M-10) from the preceding        FIG. 15, and also the structure of this polymer once the oxazine        rings thereof have been opened (Polymer denoted by P-4′) (FIG.        17);    -   the scheme for the synthesis of a particular polybenzoxazine        (homopolymer) (Polymer denoted by P-5) according to the        invention, starting from the sole particular halogenated        benzoxazine of formula (A-11) (Monomer M-11), and also the        structure of this polymer once the oxazine rings thereof have        been opened (Polymer denoted by P-5′) (FIG. 18);    -   the scheme for the synthesis, starting from brominated phenol        (compound 1), p-formaldehyde (compound 3) and another specific        aliphatic diamine (compound 4), of a particular brominated        dibenzoxazine of formula (A-12) (Monomer denoted by M-12) that        can be used for the synthesis of polybenzoxazines (Polymer P-6        and P-6′ from FIG. 20) in accordance with the invention (FIG.        19);    -   the scheme for the synthesis of a particular polybenzoxazine        (homopolymer) (Polymer denoted by P-6) according to the        invention, starting from the sole particular halogenated        benzoxazine of formula (A-12) (Monomer M-12), and also the        structure of this polymer once the oxazine rings thereof have        been opened (Polymer denoted by P-6′) (FIG. 20);    -   another possible scheme for obtaining the preceding Polymer P-6,        by direct synthesis (starting from the compounds 3, 4 and 5),        i.e. without passing through the preceding Monomer M-12 (FIG.        21);    -   the scheme for the synthesis of a particular polybenzoxazine        (Polymer denoted by P-7) according to the invention, starting        from the preceding particular halogenated benzoxazine of formula        (A-11) (Monomer M-11) and from the preceding particular monomer        of formula (A-12) (Monomer M-12), and also the structure of this        polymer once the oxazine rings thereof have been opened (Polymer        denoted by P-7′) (FIG. 22).

4. DETAILED DESCRIPTION OF THE INVENTION

Unless expressly indicated otherwise, all the percentages (%) indicatedin the present application are percentages by mass (or by weight, in anequivalent manner).

The expression “x and/or y” means “x” or “y” or both (i.e. “x and y”).Any range of values denoted by the expression “between a and b”represents the field of values ranging from more than “a” to less than“b” (that is to say limits “a” and “b” excluded), whereas any range ofvalues denoted by the expression “from a to b” means the field of valuesranging from “a” up to “b” (that is to say including the strict limits“a” and “b”).

It will firstly be recalled that benzoxazines are compounds of generalformula:

The appended FIG. 1a recalls the general principle for the synthesis ofa benzoxazine, here starting from (condensation reaction) one moleculeof phenol, two molecules of formaldehyde and an amine (R denoting theresidue of the amine), with elimination of two molecules of water.

FIG. 1b itself recalls the (ring-opening) mechanism for opening theoxazine ring of such a compound during a heat input (represented by thesymbol A).

Numerous benzoxazine compounds or monomers can thus be synthesized usingvarious phenols and amines depending on their types of substituents.These groups of substituents may then provide polymerizable sites andenable the synthesis of various benzoxazine polymers (orpolybenzoxazines).

Benzoxazines and polybenzoxazines which are derived therefrom areproducts that are nowadays well known to a person skilled in the art; tocite but a few publication examples, mention may be made of the articles“Polybenzoxazines—New high performance thermosetting resins: synthesisand properties”; N. N. Ghosh et al., Prog. Polym. Sci. 32 (2007),1344-1391, or “Recent Advancement on Polybenzoxazine—A newly DevelopedHigh Performance Thermoset”, Y. Yaggi et al., J. Polym. Sci. Part A:Polym. Chem., Vol. 47 (2009), 5565-5576, and also for example thepatents or patent applications U.S. Pat. No. 5,543,516, WO 2013/148408.

As explained in detail in the above documents, polybenzoxazines have theremarkable ability, at high temperature (for example typically above150° C. or even above 200° C. depending on their particularmicrostructure) to open their oxazine rings and to thus result inthermosetting polyphenolic resin structures.

The specific polybenzoxazine of the invention derives from a benzoxazine(referred to as Monomer M in the present application) of halogenatedtype that corresponds to the following generic formula (A), Halrepresenting a (at least one, i.e. one or more) halogen:

FIG. 2 gives the general scheme for the synthesis thereof, under heatinput (A) and with elimination of water, starting from a halogenatedphenol, p-formaldehyde and a diamine.

In the formula (A) above, Z (like Z₁ and Z₂ described below) representsa bonding group (spacer) that is at least divalent, that is to say thatit could comprise more than two covalent bonds, for example three orfour covalent bonds. Preferably, Z (like Z₁ and Z₂ described below) isdivalent, that is to say comprises only two covalent bonds.

Z (like Z₁ and Z₂ described below) may be aliphatic, cycloaliphatic oraromatic. This group, which may be ethylenically saturated orunsaturated, by definition comprises at least one (i.e. one or more)carbon atom, and optionally at least one (i.e. one or more) heteroatomchosen from O (oxygen), S (sulfur), N (nitrogen) and P (phosphorus).

According to one preferential embodiment of the invention, Z (like Z₁and/or Z₂ described below) represents an aliphatic group comprising from1 to 20, more preferentially from 1 to 16, in particular from 1 to 12carbon atoms, or else a cycloaliphatic group comprising from 3 to 20,more preferentially from 3 to 16, in particular from 3 to 12 carbonatoms. More preferentially still, Z (like Z₁ and/or Z₂ described below)represents an alkylene group comprising from 1 to 20, preferably from 1to 16, in particular from 1 to 12 carbon atoms.

More preferentially, Z (like Z₁ and/or Z₂ described below) comprises atleast one group selected from —(CH₂)_(x)—, —CH₂-Ph-CH₂—,—(CH₂—CH₂—X)_(n)— and —(CH(CH₃)—CH₂—X)_(n)—, “x” and “n” being integersfrom 1 to 20, in particular from 1 to 16, more particularly from 1 to12, Ph representing the benzene ring, and X representing at least one(i.e. one or more) heteroatom chosen from O (oxygen), S (sulfur), N(nitrogen) and P (phosphorus).

Each benzene ring of the Monomer M bears at least one (i.e. one or more)halogen. Moreover, in this monomer of formula (A), one or more hydrogenatoms of at least one or each benzene ring may (optionally) besubstituted by various substituents, for example by functional groupscapable of promoting the adhesion of the polymer to the metal and/or tothe rubber.

Preferably, each benzene ring of the monomer M bears a single halogen(Hal) or at most two, more preferentially one and only one halogen, thelatter being more preferentially located in the para position to theoxygen of the oxazine ring.

According to one particularly preferential embodiment, which can becombined with each of the other embodiments of the invention, Halrepresents bromine.

FIG. 3 illustrates a possible scheme for the synthesis, starting from aspecific diamine of aliphatic type (polyethylene diamine), of aparticular halogenated benzoxazine of formula (A-1), this benzoxazinebeing able to be used as monomer (Monomer denoted by M-1) for thesubsequent synthesis of a polybenzoxazine in accordance with theinvention. It is noted that Z represents here a —(CH₂)_(x)— methylenegroup in which the symbol “x” represents an integer that preferablyvaries from 1 to 20, more preferentially from 1 to 16, in particularfrom 1 to 12. Such a synthesis will be exemplified later for theobtaining of a specific monomer (Monomer M-10; FIG. 15 and FIG. 16).

According to another preferred embodiment, Z (like Z₁ and/or Z₂described below) represents an aromatic group comprising from 6 to 30,more preferably from 6 to 20, carbon atoms. Thus, FIG. 4 illustratesanother possible scheme for the synthesis, this time starting from aspecific diamine of aromatic type (p-xylylene diamine), of anotherexample of a particular halogenated benzoxazine of formula (A-2), thatcan be used as monomer (Monomer denoted by M-2) for the subsequentsynthesis of another polybenzoxazine in accordance with the invention.

FIGS. 5, 6 and 7 illustrate three other possible schemes for thesynthesis, always starting from a halogenated phenol andparaformaldehyde on the one hand and, on the other hand, from variousspecific diamines, all of aliphatic type, of other examples ofparticular benzoxazines of respective formulae (A-3), (A-4) and (A-5)that can be used as monomers (Monomers respectively denoted by M-3, M-4and M-5) for the synthesis of polybenzoxazines in accordance with theinvention.

In FIG. 5, the repetition of the (polyethylene oxide) [—CH₂—CH₂—O—]units on the bonding group Z is capable of resulting in polybenzoxazinesof high crystallinity, whilst in FIG. 6, the presence of the(polypropylene oxide) methyl groups on Z makes it possible to reduce thereactivity of the two amine end groups and to result in polybenzoxazinesof lower crystallinity. In FIG. 7, the presence on the spacer Z of thesulfur atom (heteroatom) in the (polyethylene thioether) [—CH₂—CH₂—S—]repeat units, is capable of further improving the adhesion of thepolybenzoxazine to metal. Thus, it can be seen that the structure of theZ (like Z₁ and Z₂ described below) group of the benzoxazine monomer maybe modified considerably with the aim of adjusting the properties of thefinal polymer. This constitutes a major advantage of the presentinvention.

FIG. 8 illustrates another possible scheme for the synthesis, startingfrom a halogenated phenol, paraformaldehyde and a specific aliphaticpolyamine consisting this time of a triamine (tris(3-aminopropyl)amine),of another example of a particular halogenated (tri)benzoxazine compoundof formula (A-6) that can be used as a monomer (Monomer denoted by M-6)for the synthesis of another polybenzoxazine according to the invention.

The polybenzoxazine of the invention (Polymer P) therefore has theessential feature of comprising structural repeating units comprising atleast one unit corresponding to the formula (I) (before opening of theoxazine rings) or formula (II) (after ring opening) below:

in which Z₁ and Z₂, which are identical or different, represent abonding group (spacer) that is at least divalent and aliphatic,cycloaliphatic or aromatic, comprising at least one carbon atom andoptionally at least one heteroatom chosen from O, S, N and P.

A polymer should be understood here as any homopolymer or copolymer, inparticular block copolymer, with repeating structural units comprisingat least one unit of formula (I) or (II) above; the polymer of theinvention may of course comprise both units of formula (I) and units offormula (II).

In formula (II) above, a person skilled in the art will immediatelyunderstand that the symbols “*” (which are identical or different)represent any attachment of the unit to a carbon atom or to a heteroatom(preferably chosen from O, S, N and P), which attachment or bond resultsfrom the opening of the oxazine rings.

It will of course be understood that Z₁ and Z₂ have the main definitionsand the preferential definitions already described in detail above for Zin the benzoxazine (monomer) compound.

Thus, according to one preferential embodiment, Z₁ and/or Z₂, which areidentical or different, represent an aliphatic group comprising from 1to 20, preferably from 1 to 16 carbon atoms, or a cycloaliphatic groupcomprising from 3 to 20, preferably from 3 to 16 carbon atoms, andoptionally at least one heteroatom chosen from O, S, N and P.

More preferentially, Z₁ and/or Z₂, which are identical or different,represent an alkylene group comprising from 1 to 20, preferably from 1to 16, in particular from 1 to 12 carbon atoms, and optionally at leastone heteroatom chosen from O, S, N and P.

According to another preferential embodiment, Z₁ and/or Z₂, which areidentical or different, represent an aromatic group comprising from 6 to30, preferably from 6 to 20 carbon atoms, and optionally at least oneheteroatom chosen from O, S, N and P.

According to another preferential embodiment, Z₁ and/or Z₂ comprise atleast one group selected from —(CH₂)_(x)—, —CH₂-Ph-CH₂—,—(CH₂—CH₂—X)_(n)— and —(CH(CH₃)—CH₂—X)_(n)—, “x” and “n” being integersfrom 1 to 20, in particular from 1 to 16, more particularly from 1 to12, (“x” being denoted more specifically as “x₁” in the case of Z₁ anddoes “x₂” in the case of Z₂), Ph representing the benzene ring, and Xrepresenting at least one (i.e. one or more) heteroatom chosen from O(oxygen), S (sulfur), N (nitrogen) and P (phosphorus).

FIG. 9 represents a general scheme for the synthesis, bypolycondensation, of a polybenzoxazine (Polymer P) according to theinvention, starting from the halogenated benzoxazine of formula (A) fromFIG. 2 (Monomer M) and from another monomer (Monomer M′), of genericformula denoted by (A′) which is very similar and, which may bedistinguished in particular by the nature of its spacer (Z₂) and/or ofits halogen (Hal).

The polybenzoxazine “P” from FIG. 9, more precisely at least some of itsrepeat units, has also been represented in FIG. 13, before (Polymer P)and after (Polymer P′) the opening of its oxazine rings.

FIG. 10 represents a particular scheme for the synthesis of such apreferential polybenzoxazine according to the invention (Polymer denotedby P-1) of formula (I-1), starting from a particular halogenatedbenzoxazine (Monomer M-7) of formula (A-7) and from another particularhalogenated benzoxazine (Monomer M-7′) of formula (A-7′) which is verysimilar and which may be distinguished in particular by the value of theinteger “x” (respectively “x₁” and “x₂” for Z₁ and Z₂).

In this example, it is noted in particular, according to one preferredembodiment of the invention already described, that each benzene ring ofthe monomers M-7 and M-7′ bears one and only one halogen (Hal), morepreferentially bromine, this halogen being more particularly located inthe para position to the oxygen of the oxazine ring.

This polybenzoxazine from FIG. 10, or more precisely at least some ofits repeat units, has also been represented in FIG. 14, before (PolymerP-1) and after (Polymer P-1′) the opening of its oxazine rings followinga sufficient heat input.

FIG. 11 represents another particular scheme for the synthesis ofanother specific polybenzoxazine (Polymer denoted by P-2) according tothe invention, of formula (I-2), starting from the preceding specifichalogenated benzoxazine (Monomer M-7) and from another specificbenzoxazine (Monomer M-8) of formula (A-8), of aromatic type with regardto the spacer Z₂.

FIG. 12 represents another particular scheme for the synthesis ofanother specific polybenzoxazine (Polymer denoted by P-3) according tothe invention, of formula (I-3), starting from the preceding specifichalogenated benzoxazine (Monomer M-7) and from another specificbenzoxazine of formula (A-9) (Monomer M-9) of aliphatic type (withheteroatom O) with regard to the spacer Z₂.

In these examples from FIGS. 11 and 12, as for the preceding FIG. 10, itis noted in particular, according to one preferred embodiment of theinvention already indicated, that each benzene ring of the benzoxazinemonomers bears one and only one halogen (Hal), more preferentiallybromine, located more particularly in the para position to the oxygen ofthe oxazine ring.

As already indicated, FIGS. 13 and 14 also represent polybenzoxazinesaccording to the invention (here respectively denoted by P′ and P-1′)from FIG. 9 and FIG. 10, once their oxazine rings are open after heatinput.

FIGS. 15 and 16 represent the scheme for the synthesis, starting frombrominated phenol (compound 1), p-formaldehyde (compound 3) and aspecific aliphatic diamine (compound 2), of a particular brominateddibenzoxazine of formula (A-10) (Monomer denoted by M-10) that can beused for the synthesis of polybenzoxazines (Polymer P-4 and P-4′ fromFIG. 17) in accordance with the invention, and also the ¹H NMR spectrum(500 MHz) of Monomer M-10 dissolved in CD₂Cl₂. These figures will becommented upon in detail later on.

FIGS. 17 and 18 represent two other possible schemes for the synthesisof specific polybenzoxazines according to the invention (Polymersdenoted respectively by P-4 and P-5, of respective formulae (I-4) and(I-5), starting from a single brominated benzoxazine (homopolymerizationrespectively of the Monomers M-10 and M-11 of respective formulae (A-10)and (A-11)), and a heat input (A), and also these same polymers once theoxazine rings thereof have been opened (Polymer P-4′ and P-5′).

FIG. 19 represents the scheme for the synthesis, starting frombrominated phenol (compound 1), p-formaldehyde (compound 3) and anotherspecific aliphatic diamine (compound 4), of a particular brominateddibenzoxazine of formula (A-12) (Monomer denoted by M-12) that can beused for the synthesis of polybenzoxazines (Polymer P-6 and P-6′ fromFIG. 20 which follows) in accordance with the invention.

FIG. 20 represents the scheme for the synthesis of another particularpolybenzoxazine according to the invention (Polymer denoted by P-6),starting from the sole particular halogenated benzoxazine of formula(A-12) (Monomer M-12), and also the structure of this polymer once theoxazine rings thereof have been opened (Polymer denoted by P-6′).

Another scheme for obtaining the Polymer P-6 above is represented inFIG. 21, this time by direct synthesis (starting from the compounds 3, 4and 5) i.e. without passing through the preceding Monomer M-12 (FIG.21); this figure will be commented upon in detail later on.

Lastly, FIG. 22 represents another example of a scheme for the synthesis(copolymerization) of another particular polybenzoxazine according tothe invention (Polymer denoted by P-7), starting from the precedingbrominated benzoxazine of formula (A-11) (Monomer M-11) and from thepreceding benzoxazine, itself also brominated, of formula (A-12)(Monomer M-12), and also the structure of this polymer once the oxazinerings thereof have been opened (Polymer denoted by P-7′).

Typically, the polybenzoxazine of the invention may comprise from ten toseveral hundred, preferably from 50 to 300 structural units having unitsof formula (I) and/or (II), in particular structural units asrepresented as examples in FIGS. 10 to 14, 17 and 18 and 20 to 22.

The polybenzoxazine of the invention can advantageously be used, asadhesion primer or as sole adhesive layer, for coating a metalsubstrate, at the very least a substrate at least the surface of whichis at least partially metallic, and adhering in particular thissubstrate to rubber.

The invention also relates to such a substrate, in particular made ofsteel such as a carbon steel. The steel could be bright (i.e. uncoated)steel, or else may be coated at least partially with at least one layer(therefore intermediate layer, positioned between steel andpolybenzoxazine layer) of a second metal, referred to as surface metal,selected from the group consisting of aluminium, copper, zinc and alloysof at least one of these metals with at least one other metal (which mayor may not belong to this group). This surface metal is in particularbrass.

In order to adhere the rubber to the polybenzoxazine layer, use could bemade of any known adhesive system. Use will be made for example of aconventional textile adhesive of “RFL” type comprising at least onediene elastomer such as natural rubber, or any equivalent adhesive knownfor imparting satisfactory adhesion between rubber and conventionalpolymers such as polyester or polyamide, such as for example theadhesive compositions described in the patent applications WO2013/017421, WO 2013/017422, WO 2013/017423, WO 2015/007641, WO2015/007642.

Before the above adhesive coating process, it might be advantageous toactivate the surface of the polymer of the invention, for examplephysically and/or chemically, to improve the adhesive uptake thereofand/or the final adhesion thereof to the rubber. A physical treatmentcould consist, for example, of a treatment by radiation such as anelectron beam, or by plasma; a chemical treatment could consist, forexample, of prior passage through a bath of epoxy resin and/orisocyanate compound.

A person skilled in the art will readily understand that the connectionbetween the metal substrate provided with its polybenzoxazine layer andthe rubber layer with which it is in contact will be definitivelyprovided during the final curing (crosslinking) of the rubber article inquestion.

5. EXEMPLARY EMBODIMENTS OF THE INVENTION

The following tests describe in detail examples of the synthesis ofbenzoxazine compounds (Monomers M-70 and M-12) and of polybenzoxazines(Polymers P-4 and P-6) according to the invention. Lastly, adhesiontests are carried out in order to illustrate the excellent adhesiveperformance of the polybenzoxazines of the invention.

Generally, before any (monomer or polymer) synthesis, the apparatus usedis dried under vacuum (50 mbar) at at least 100° C. (hot air gun) for atleast 5 min, then cooled to room temperature (20° C.) and placedcontinuously under a stream of inert gas (nitrogen). All the productsused are initially weighed and handled under an argon atmosphere in aglove box, then transferred under a stream of argon into the reactionflask.

5.1. Synthesis of a Halogenated Benzoxazine Compound (Monomer M-8)

The synthesis is carried out according to the procedure depicted in FIG.15, as explained in detail below, starting from three compounds: ahalogenated phenol (compound 1; 4-bromophenol; Aldrich product“B75808”), an aliphatic diamine (compound 2; 1,8-diaminooctane; Aldrichproduct “D22401”) and a p-formaldehyde (compound 3; Aldrich “158127”product), in the presence of two solvents (anhydrous toluene andanhydrous ethanol).

For this synthesis, a 250-ml three-neck round-bottomed flask, equippedwith a thermometer, a nitrogen inlet, a magnetic stirrer and a condenseris provided. Compound 1 (2 eq; 10.38 g, i.e. 60 mmol) then ethanol (51ml) are poured into the round-bottomed flask. The presence of ethanol isimportant here, preventing the formation of an unstable triazine-typeintermediate product. While stirring, compound 2 (1 eq; 4.32 g, i.e. 30mmol), compound 3 (4 eq; 3.60 g, i.e. 120 mmol) and finally the toluene(102 ml) are then introduced. The reaction medium is heated (around 75°C.) at reflux for 72 h, then placed on a rotary evaporator, at 50° C.under vacuum (50 mbar), to evaporate the solvents. Alemon-yellow-coloured oil is thus obtained.

This oil then undergoes a first purification on an SiO₂ column, with theaid of a diethyl ether/cyclohexane eluent, in a volume ratio of the twosolvents that varies from 10:35 (initial) to 10:20 (final). The purifiedfractions containing the monomer (M-10) are recombined and the solventsare evaporated. A light yellow solid is thus obtained. The latter isplaced in methanol (1 g per 80 ml) and heated at reflux (65° C.) for 30min. The solution is then left to cool to ambient temperature (around20° C.) for crystallization of the monomer. The solid product obtainedis isolated by filtration (Buchner filter). White-coloured crystals arethus obtained, which are dried in a vacuum oven at 50° C., overnight, toeliminate any trace of solvent (reaction yield of around 60%).

The ¹H NMR spectrum (500 MHz) of the Monomer M-10 thus synthesized,dissolved in CD₂Cl₂, is reproduced in the appended FIG. 16. This NMRanalysis gives the following results:

¹H MMR (500 MHz) CD₂Cl₂: 1.29 (m, 8H); 1.51 (m, 4H); 2.67 (m, 4H); 3.92(s, 4H); 4.82 (s, 4H); 6-62-6-64-(d, 2H); 7.08 (s, 2H); 7.17-7.19 (d,2H).

5.2. Synthesis of a Polybenzoxazine (Polymer P-4)

This synthesis is carried out according to the procedure depicted in theFIG. 17, as described in detail below, starting from the solebenzoxazine monomer obtained in the preceding step (Monomer M-10); thisbeing in the presence of 2,2′-bipyridyl (Sigma Aldrich product“D216305”); 1,5-cyclooctadiene (Sigma Aldrich “246050”);[bis(1,5-cyclooctadiene)nickel(0)], Ni(COD)2 (Sigma Aldrich “244988”);anhydrous solvents: toluene (Sigma Aldrich “179418”) andN,N-dimethylformamide (DMF, Acros product ref. “348431000”). The monomerM-10 was dried beforehand under vacuum at 40° C., overnight.

The synthesis is carried out in a 50-ml four-neck round-bottomed flask,equipped with a nitrogen inlet, a thermometer, a magnetic stirrer and acondenser and a distillation bridge (provided with a heating mantle).Firstly 2,2′-bipyridyl (61.08 mg i.e. 0.391 mmol), and next1,5-cyclooctadiene (27.8 mg i.e. 0.257 mmol) and the catalyst Ni(COD)₂(103.75 mg i.e. 0.377 mmol) are introduced into the round-bottomedflask. Added next are 15 ml of DMF with stirring, then 5 ml of toluene.Everything is purged under N₂ for 5 min and the reaction medium isheated to 80° C. for 30 min. Finally, the Monomer M-10 (0.2 g i.e. 0.377mmol) of formula (A-10) is added with stirring. Everything is left toreact at 80° C. for 72 h. The volatile products of the reaction mixtureare then distilled at 80° C. (under 50 mbar); the polymer obtained iswashed 3 times in 20 ml of an acetone/methanol (1:1) mixture, isolatedby filtration (Buchner funnel), washed again with 20 ml of distilledwater and finally dried under vacuum at 80° C. overnight (around 12 h).

The Polymer P-4 from FIG. 17 was thus obtained, as attested to by theATR FTIR (Attenuated Total Reflection; Fourrier Transform InfraredSpectroscopy) analysis, which revealed typical transitions at thefollowing frequencies [in cm⁻¹]:

2847.6; 1609.9; 1483.8; 1435.9; 1220.2; 1114.8; 1018.0; 926.3; 813.5;438.7.

To be thorough, it was observed that such a polymerization of theMonomer M-10 to Polymer P-4 was accompanied by the completedisappearance, relative to the corresponding spectrum of the MonomerM-10, of the peaks initially present at the frequencies (in cm⁻¹) of608.6; 740.8; 850.5 and 1170.1, whilst the peaks at 915.5 and 1475.3were shifted respectively to 926.3 and 1483.8.

This Polymer P-4, in the form of a beige-coloured powder, was alsoanalyzed by DSC (Differential Scanning Calorimetry) between −80° C. and+250° C. with a ramp of 10° C./min (Mettler Toledo DSC “822-2”apparatus; nitrogen atmosphere): the analysis revealed, in the firstpass between −80° C. and +250° C., an exothermicity (corresponding tothe opening of the oxazine rings and to the crosslinking of the polymer)above 200° C., with a maximum at around 230° C. During the second andthird DSC passes, still conducted between −80° C. and +250° C., no glasstransition (Tg) was visible, which attests to the very high thermalstability of the polymer of the invention.

5.3. Synthesis of Another Halogenated Benzoxazine Compound (MonomerM-12)

The synthesis is carried out according to the procedure depicted in FIG.19 as explained in detail below, starting from three compounds: ahalogenated phenol (compound 1; 4-bromophenol; Aldrich product“B75808”), an aliphatic polyether diamine (compound 4; a poly(propyleneglycol) bis(2-aminopropyl ether) (Mn equal to 400; Aldrich product“406678”) and a p-formaldehyde (compound 3; Aldrich product “158127”),in the presence of two solvents (anhydrous toluene and anhydrousethanol).

As before, for this synthesis, a 250-ml three-neck round-bottomed flask,equipped with a thermometer, a nitrogen inlet, a magnetic stirrer and acondenser is provided. Compound 1 (2 eq; 10.49 g i.e. 60 mmol) thenethanol (51 ml) are poured into the round-bottomed flask. Whilestirring, compound 4 (1 eq; 12.62 g i.e. 30 mmol), compound 3 (4 eq;3.79 g i.e. 120 mmol) and finally the toluene (102 ml) are thenintroduced. The reaction medium is heated at reflux (around 75° C.) for48 h, then placed under vacuum (1 mbar) at 110° C. for 30 min to ensurethe evaporation of the volatile products. An orange-coloured viscousliquid is thus obtained. No trace of free bromophenol compound wasdetected by FTIR spectroscopy in the reaction product.

The ¹H NMR spectrum (500 MHz) of the Monomer M-12 thus synthesized,dissolved in CD₂Cl₂, confirmed its chemical structure, this NMR analysisgiving the following results:

¹H MMR (500 MHz) CD₂Cl₂: 1.12 (s, 24H); 3.10 (s, 2H); 3.31-3.56 (m,24H); 4.04 (s, 4H); 4.93 (s, 4H); 6.61-6.63 (d, 2H); 7.08 (s, 2H);7.17-7.18 (d, 2H).

5.4. Synthesis of Another Polybenzoxazine (Polymer P-6)

This synthesis is carried out according to the procedure depicted inFIG. 20, as described in detail below, starting from the solebenzoxazine monomer (Monomer M-12) obtained in the preceding step, thisbeing in the presence of 2,2′-bipyridyl (Sigma Aldrich product“D216305”); 1,5-cyclooctadiene (Sigma Aldrich “246050”);bis(1,5-cyclooctadiene)nickel(0), Ni(COD)₂ (Sigma Aldrich “244988”);anhydrous solvents: toluene (Sigma Aldrich “179418”) andN,N-dimethylformamide (DMF, Acros Organics product “348431000”). Themonomer M-12 was dried beforehand under vacuum at 60° C. overnight(around 12 h).

The synthesis is carried out in a 50-ml four-neck round-bottomed flask,equipped with a nitrogen inlet, a thermometer, a magnetic stirrer, acondenser and a distillation bridge (provided with a heating mantle).Firstly the compound 2,2′-bipyridyl (610.8 mg i.e. 3.91 mmol), and next1,5-cyclooctadiene (278 mg i.e. 2.57 mmol) and the catalyst Ni(COD)₂(1.04 g i.e. 3.77 mmol) are introduced into the round-bottomed flask,all these products being transferred under a stream of argon into thereaction flask. Added next are 150 ml of DMF with stirring, then 50 mlof toluene. Everything is purged under N₂ for 5 min and the reactionmedium is heated to 80° C. (30 min). Finally, the Monomer M-12 (3.07 gi.e. 3.77 mmol) of formula (A-12) is added with stirring. Everything isleft to react at this temperature for 72 h.

The volatile products of the reaction mixture are then distilled at 80°C. (under 50 mbar); the polymer obtained is washed 3 times in 20 ml ofan acetone/methanol (1:1) mixture, isolated by filtration (Buchnerfunnel), and finally dried under vacuum at 60° C. overnight (around 12h).

The ¹H NMR spectrum (500 MHz) of the Polymer P-6 thus synthesized,dissolved in CD₂Cl₂, confirmed its chemical structure, this NMR analysisgiving the following results:

¹H MMR (500 MHz) CD₂Cl₂: 1.08 (m, 18H); 3.36 (s, 2H); 3.41-3.56 (m,24H); 4.09 (s, 4H); 4.95 (s, 4H); 6.74-6.76 (d, 2H); 7.12 (s, 2H);7.23-7.24 (d, 2H).

5.5. Another Example of the Synthesis of the Polymer P-6

During an additional test, the preceding polymer P-6 was obtained by aprocess of direct synthesis, without this time passing through theMonomer M-12.

For this synthesis, a 250-ml three-neck round-bottomed flask, equippedwith a thermometer, a nitrogen inlet, a magnetic stirrer and a condenseris provided. The synthesis was carried out according to the proceduredepicted in FIG. 21, as explained in detail below, starting from threecompounds: an aromatic diphenol (compound 5; 4,4′-dihydroxybiphenyl;Aldrich product “168734”), a poly(propylene glycol)bis(2-aminopropylether) (compound 4) and the p-formaldehyde (compound 3;Aldrich product “158127”), in the presence of two solvents (anhydroustoluene and anhydrous ethanol).

Compound 5 (1 eq; 3.84 g i.e. 20 mmol) then ethanol (34 ml) are pouredinto the round-bottomed flask. While stirring, compound 4 (1 eq; 8.41 gi.e. 20 mmol), compound 3 (4 eq; 2.40 g i.e. 80 mmol) and finally thetoluene (68 ml) are then introduced. The reaction medium is heated(around 75° C.) at reflux for 24 h, then placed on a rotary evaporator,at 50° C. under vacuum (50 mbar) to evaporate the solvents. Alemon-yellow-coloured viscous oil is thus obtained.

The ¹H NMR spectrum (500 MHz) of the Polymer P-6 thus synthesized,dissolved in CD₂Cl₂, confirmed its chemical structure, this NMR analysisgiving the following results:

¹H MMR (500 MHz) CD₂Cl₂: 1.09 (m, 18H); 3.36 (s, 2H); 3.41-3.56 (m,24H); 4.09 (s, 4H); 4.94 (s, 4H); 6.74-6.75 (d, 2H); 7.12 (s, 2H);7.23-7.24 (d, 2H).

5.6. Test of Adhesion in a Metal/Rubber Composite

A portion (650 mg) of the Polymer P-6 previously prepared was dissolvedin 8 ml of toluene, in order to form a slightly yellow transparentsolution, a fraction (0.7 ml) of which was then deposited uniformly on abrass tape (film) having dimensions of 10 cm×2.5 cm and a thickness of0.3 mm. The assembly was placed in an oven at 175° C. (with airventilation) for 5 min under vacuum (50 mbar) (change to bright yellow),then an additional 2.5 min at 230° C. under air in order to at leastpartially open (i.e. completely or partially open) the oxazine rings ofthe polymer, this last step being accompanied by a pronounced change inthe colour of the polymer, which changes from bright yellow to a browncolour. After cooling to ambient temperature, the tape provided at thesurface with its thin (5 to 10 μm thick) layer of polybenzoxazine thusformed, was then coated by brush with an aqueous composition of RFLadhesive (around 81% by weight of water) based on resorcinol (around2%), on formol (around 1%) and on a rubber latex (around 16% of NR, SBRand VP-SBR rubbers). It was dried for 30 s; at 80° C. in order toeliminate the water, then treated in an oven for 2.5 min at 230° C.

The brass tape thus coated with the polybenzoxazine film then coatedwith adhesive, was subsequently placed between two layers ofconventional rubber composition for a belt reinforcement of a passengervehicle tyre, said composition based on natural rubber, on carbon blackand silica as filler and on a vulcanization system (sulfur andsulfenamide accelerator); this composition being devoid of cobalt salt.The metal/rubber composite test specimen thus prepared was then placedunder a press and everything was cured (vulcanized) at 165° C. for 15min under a pressure of 20 bar. After vulcanization of the rubber,excellent adhesive bonding between the rubber matrix and metal tape wasobtained, despite the absence of cobalt salt in the rubber matrix; thisis because, during peel tests (at 20° C.), it was found that the failureoccurred systematically in the rubber matrix itself and not at theinterface between metal and rubber.

Other adhesive bonding tests were carried out on a(n) (uncoated) brightsteel tape; they too revealed an excellent adhesion to the rubber(systematic failure in the rubber matrix).

In conclusion, the polybenzoxazine according to the invention offers themetallic substrates the major advantage of being able subsequently to beadhesively bonded to rubber matrices using simple textile adhesives,such as RFL adhesives, or else directly (that is to say, withoutemploying such adhesives) to these rubber matrices, for example when thelatter contain appropriate functionalized unsaturated elastomers, suchas epoxidized elastomers.

Thus, use may be made of metal substrates optionally coated withadhesive metal layers such as brass, and also surrounding rubbermatrices devoid of metal salts, in particular of cobalt salts.

Moreover, this constituting a significant advantage compared to theother known polymers described in the introduction to the presentdocument, polybenzoxazines of the invention have the remarkable ability,at high temperature, to open their oxazine rings and to thus result in athermosetting polyphenolic resin structure. This gives them a betterthermal stability, with no visible phase transition at temperaturesabove 200° C. Lastly, their specific microstructure makes it possible,very advantageously, to adjust the flexibility of the molecule dependingon the particular applications targeted.

The invention claimed is:
 1. A polybenzoxazine, the repeat units ofwhich comprise at least one unit corresponding to the formula (I) or(II):

wherein Z₁ and Z₂ are different one of Z₁ and Z₂ represents an aliphaticgroup comprising from 1 to 20 carbon atoms or a cycloaliphatic groupcomprising from 3 to 20 carbon atoms, and optionally at least oneheteroatom chosen from O, S, N and P, and the other of Z₁ and Z₂represents an aromatic group comprising from 6 to 30 carbon atoms, andoptionally at least one heteroatom chosen from O, S, N and P.
 2. Thepolybenzoxazine according to claim 1, wherein the one of Z₁ and Z₂represents an alkylene group comprising from 1 to 20 carbon atoms, andoptionally at least one heteroatom chosen from O, S, N and P.
 3. Apolybenzoxazine, the repeat units of which comprise at least one unitcorresponding to the formula (I) or (II):

wherein one of Z₁ and Z₂ comprises a group selected from the groupconsisting of —(CH₂)_(x)—, —CH₂-Ph-CH₂—, —(CH₂—CH₂—X)_(n)— and—(CH(CH₃)—CH₂—X)_(n)—, wherein x and n are integers from 1 to 20, Phrepresents a benzene ring, and X represents at least one heteroatomchosen from oxygen, sulfur, nitrogen and phosphorus, and wherein theother of Z₁ and Z₂ represents an aromatic group comprising from 6 to 30carbon atoms, and optionally at least one heteroatom chosen from O, S, Nand P.
 4. A coating for a substrate, at least the surface of which is atleast partially metallic, comprising a polybenzoxazine, the repeat unitsof which comprise at least one unit corresponding to the formulae (I) or(II):

wherein Z₁, Z₂, or both Z₁ and Z₂, which are identical or different,represent an aromatic group comprising from 6 to 30 carbon atoms, andoptionally at least one heteroatom chosen from O, S, N and P, andwherein, when Z₁ and Z₂ are different, one of Z₁ and Z₂ is as definedabove and one of Z₁ and Z₂ represents an at least divalent, aliphatic,cycloaliphatic or aromatic bonding group comprising at least one carbonatom and optionally at least one heteroatom selected from O, S, N and P.5. A method of bonding metal to rubber comprising: coating a substrate,at least the surface of which is at least partially metallic, with asubstrate coating comprising a polybenzoxazine, the repeat units ofwhich comprise at least one unit corresponding to the formulae (I) or(II):

wherein Z₁, Z₂, or both Z₁ and Z₂, which are identical or different,represent an aromatic group comprising from 6 to 30 carbon atoms, andoptionally at least one heteroatom chosen from O, S, N and P, andwherein, when Z₁ and Z₂ are different, one of Z₁ and Z₂ is as definedabove and one of Z₁ and Z₂ represents an at least divalent, aliphatic,cycloaliphatic or aromatic bonding group comprising at least one carbonatom and optionally at least one heteroatom selected from O, S, N and P.6. A substrate, at least the surface of which is at least partiallymetallic, wherein the at least partially metallic portion is coated witha polybenzoxazine, the repeat units of which comprise at least one unitcorresponding to the formulae (I) or (II):

wherein Z₁, Z₂, or both Z₁ and Z₂, which are identical or different,represent an aromatic group comprising from 6 to 30 carbon atoms, andoptionally at least one heteroatom chosen from O, S, N and P, andwherein, when Z₁ and Z₂ are different, one of Z₁ and Z₂ is as definedabove and one of Z₁ and Z₂ represents an at least divalent, aliphatic,cycloaliphatic or aromatic bonding group comprising at least one carbonatom and optionally at least one heteroatom selected from O, S, N and P.7. The substrate according to claim 6, wherein the substrate is made ofsteel.
 8. The substrate according to claim 7, wherein the substrate ismade of carbon steel.
 9. The substrate according to claim 7, wherein thesteel is a bright steel.
 10. The substrate according to claim 7, whereinthe steel is at least partially coated with at least one layer of asecond metal selected from the group consisting of aluminium, copper,zinc and alloys of at least one of these metals.
 11. The substrateaccording to claim 10, wherein the at least one layer of a second metalcomprises brass.